The present invention relates to a technique for providing relatively normal voice-grade telephone communications over the signaling data (D) channel of a digital subscriber line, while essentially all of the bearer (B) channel capacity is engaged for other communications, particularly data services.
Modern society continues to create exponentially increasing demands for digital information, and the communication of such information creates increasing needs for ever faster data communication speeds.
The most common form of computer-to-computer data communication in use today relies on modems and analog telephone connections. Such modems communicate data as modulated audio signals, within the voice bandwidth of the telephone network. The various elements of the telephone network treat these voice frequency signals exactly like voice type analog audio signals. This telephone-based operation provides the voice grade analog modem a unique power, the necessary connections are virtually ubiquitous. Such modems can communicate via virtually any telephone line or wireless telephone (e.g. cellular) to any other such telephone link, virtually anywhere in the world.
However, the design of the existing telephone network optimizes efficiency for communication of voice information, and as a result, places severe limitations on the capacity of modem communications. Also, use of a modem on a subscriber""s line prohibits use thereof for normal voice communications for the duration of the data session. To have voice communication capability at the same time as the data communication, the subscriber must pay for a second telephone line to the customer""s premises.
Integrated Services Digital Network (ISDN) offers faster data communications and the capacity for concurrent data and voice telephone services. For ISDN service, a user obtains a digital subscriber line (DSL) termination unit connected to the customer premises end of a telephone line. The basic rate interface (BRI) DSL terminal unit provides duplex 160 kb/s digital communication with corresponding elements in the telephone network. The 160 kb/s capacity carries two bearer (B) channels, each at 64 kb/s, one data (D) channel at 16 kb/s and overhead information contained in a 16 kb/s embedded operations channel (EOC).
The telephone network switches the B-channels through the network, using 64 kb/s synchronous time slots, in much the same way that it switches plain old telephone service (POTS) calls. B-channel data calls, however, may be switched through as end-to-end digital communications at the full 64 kb/s rate because now the digital channel rate matches the channel rate defined by the time slot interchange units within the telephone switch fabric. There are no conversions between analog and digital content within the network.
The B-channels may be used separately, for example, for one voice telephone call and one data communication. Some applications also allow aggregation of the channels, to combine the B-channels to provide data communications up to the combined rate of 128 kb/s, when there is no concurrent telephone usage. If the data application utilizes both B-channels, there is no capacity for a concurrent voice call over the same line.
ISDN Digital Subscriber Line (IDSL) is a leased line type service, which uses the 2B1Q line-coding standard for ISDN BRI circuits for data-only applications. Essentially, the two B-channels are combined and dedicated to the data service. Consequently, IDSL operates at 128 kb/s. IDSL provides this higher speed data service for line lengths up to 18,000 feet without a repeater or greater distances with ISDN repeaters, the same as standard 2B+D ISDN.
Because IDSL uses the standard ISDN line coding, customers with standard basic rate interface (BRI) type terminal adapters can use their current adapters (in a leased line mode) together with any associated equipment, for connecting to ISDL lines. At the network end of the line, the ISDL line terminates on a line card in a channel bank of a carrier system. However, instead of coupling the B-channels to a time slot interchange unit for switching in the same manner as ISDN, the carrier system connects the customer""s B-channels over two slots on a dedicated transport to a desired data point. Typically, these channels connect to a high-speed backbone network, such as a Frame Relay network, a super multi-mega-bit data service (SMDS) network or an asynchronous transfer mode (ATM) network. The link from the customer premises to the backbone network is a dedicated or xe2x80x9cnailed-upxe2x80x9d connection. The backbone network, however, provides fast packet-switched access to data communication services. In this manner, IDSL lines can provide dedicated access to the particular fast packet backbone network and through that network to the Internet, to private networks, or the like.
With the IDSL service, all communications on the subscriber""s line are dedicated to the data service. There is no available bearer capacity for any voice communication. To execute voice communications, the subscriber again must pay for an extra line from the telephone network to the customer""s premises.
A need therefore exists for an efficient technique to provide voice telephone communications over a digital subscriber line, particularly an ISDN line or IDSL line, when all of the bearer channel capacity is engaged in data communications. The additional voice capacity should require little or no modification of various network components along the subscriber line or other embedded loop plant facilities. The technique also should be readily adaptable to other types of digital subscriber line services.
The present invention addresses the above stated needs by enabling voice communication over the signaling data channel of a digital subscriber line, during communication applications that utilize the full bearer channel capacity of the line. The channel banks of a carrier system pass the bearer channel communications through in the normal manner. However, the channel bank multiplexes a number of the data channels together for communication thereof to and from a central office facility.
There have been suggestions to send voice over the D-channel of ISDN, but those have involved virtual channels and packet voice applications. The D-channel has not been used as an alternate logical path over the subscriber line to provide a voice link to an otherwise standard telephone switch nor has there been any multiplexing of D-channel voice signals for transport in a bearer channel through a carrier system.
The use of the D-channel for voice communications enables telephone service over a circuit that otherwise would not support such service, eliminating the need for the customer to buy another line for telephone traffic. The multiplexing of the low-speed D-channels enables the system to provide normal telephone service to two or more active users, while utilizing only one bearer channel or its equivalent through the carrier system. This clearly provides a more efficient utilization of the channel capacity of that system.
Thus, in one aspect, the present invention relates to a method of communicating voice-grade telephone information over a digital subscriber line. The digital subscriber line supports bearer capacity assigned to communications other than the voice-grade telephone communication. For example, the entire bearer capacity may be engaged in a data communication session. The digital subscriber line also supports a lower-speed signaling data channel. In the preferred embodiments, the bearer capacity corresponds to ISDN B-channels, and the signaling channel is an ISDN D-channel.
This communication method involves compressing the voice telephone information to the lower-speed, i.e. to the speed of the signaling channel. The compressed information is communicated over the line within the signaling data channel. The method also involves multiplexing the signaling data channel with information from at least one other signaling data channel for another subscriber line, to form multiplexed data. In the preferred embodiments, voice grade telephone data from up to four ISDN D-channels are transported in one stream multiplexed together at the B-channel or DS0 rate. The multiplexed data is transported between a channel bank coupled to the line and a switch. The compressed information of the original D-channel from the line is segregated from the multiplexed data and coupled with a voice telephone link extending through the switch to a distant telephone station. In one preferred embodiment, the D-channel streams, separated out from the multiplexed transport stream, connect to line ports of a central office telephone switch. The switch provides normal telephone service connections through the public switched telephone network.
Another aspect of the invention relates to a communication network enabling the multiplexed D-channel transport between the subscriber line and the switch that provides the telephone services. Broadly, the network comprises a transport fabric including the switch, a digital subscriber line running from a customer premises to an edge of the transport fabric, a line card for connection to the digital subscriber line at the edge of the transport fabric and a multiplexer. The line card provides throughput between a communication channel assigned to the digital subscriber line in the transport fabric and the bearer communication channel on the digital subscriber line. A multiplexer, coupled to the line card, communicates voice-grade telephone information via the D channel on the digital subscriber line and couples the D-channel and at least one other D-channel through another of the communication channels of the transport fabric of the network to the switch.
A further aspect of the invention relates to a carrier system enabling the D-channel telephone service. The system includes two channel banks and a high-speed link, such as a T1, interconnecting the channel banks.
The first channel bank comprises a line card for connection to the digital subscriber line. The line card supports a bearer communication channel and a logically separate signaling data (D) channel on the digital subscriber line. The line card provides throughput between the bearer communication channel and a first assigned communication channel on the high-speed link. The line card also has a coupling for the D channel. The first channel bank also includes a multiplexer coupled to the D channel coupling of the line card. This element of the card enables multiplexing and demultiplexing for transport of the D channel information together with other D channel information in a second assigned communication channel on the high speed link.
The second channel bank passes the first assigned channel with the bearer content between the high speed link and a port for connection to a data communications switch. In addition, the second channel bank comprises another multiplexer. This multiplexer is coupled to the second assigned channel within the high-speed link. An interface couples the D-channel information between the multiplexer in the second channel bank and a switch for voice-grade telephone service.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.